what size bottom bracket are you guys using?

[signalMTB]

in an earlier I post, I posted about some clearance issues I have now with my new crankset and rings on my 98 K2 4000. I removed the stock LX set and replaced with Carambas and blackspire rings.  The old LX appeared to have quite an offset from the distance from the rings to the BB attachment point.  My new cranks sit flat against the attachment.  The chain will not move to the big ring (46T) as it hits the front part of the swingarm, just by the pivot bolt.    See image below.

So, what size BB are you guys running on your setup?  I am thinking I need to go to 118 or 122.5 to get clearance.  Just not sure how long to go.

[Colin]

As OE on the 4000, I am running a Shimano UN71 Bottom Bracket 73 x 113mm
and a XT Derailleur and crank.
22, 34, 44, ChainRings.

Yes, looks like an offset problem on the crank......?
Is this them?
http://gallery.fakawitribe.com/CarambaAlbum/

See pics of mine:

Hopefully you can see the amount of offset, basically the middle ring ( & chain) is completely visible outside of the pivot face.

Top View - Middle Ring


Top View - Top Ring


Side View - Top Ring


Hmmmmm............Those chainrings are looking a bit worn.....................Damn! wish I hadn't looked now! <GRIN>

Col.

[signalMTB]

I was running a 113mm on my OE setup also, but the offset of the Shimano cranks allowed for clearance.   Your middle ring is looking pretty bad 

<<Yes, looks like an offset problem on the crank......?
Is this them?
http://gallery.fakawitribe.com/CarambaAlbum/>>

and yes, those are the cranks I'm running now...no offset at all. 

[RhinoDave]

When Shimano switched from square taper to Octalink  they changed how far the cranks slid onto the spindle. The conversion necessary was to go up one size from what was stock on the bike. My 856 orginally had a 110 square taper spec'd so I installed a 113 octalink . My Evo orginally spec'd a 113 square taper so the next size up was a 118. I would say since your orginal was a 113 square taper. then if you have an octalink, ISIS or later bottom bracket, you should be using a 118.

[signalMTB]

When Shimano switched from square taper to Octalink  they changed how far the cranks slid onto the spindle. The conversion necessary was to go up one size from what was stock on the bike. My 856 orginally had a 110 square taper spec'd so I installed a 113 octalink . My Evo orginally spec'd a 113 square taper so the next size up was a 118. I would say since your orginal was a 113 square taper. then if you have an octalink, ISIS or later bottom bracket, you should be using a 118.

my new BB and crankset is still square taper...I'm thinking a 119 phil wood should do the trick, or a 118 Shimano UN-54.  I'm worried a 122.5 is just too much.

I have a brand new Shimano XT UN-73 hollow spindle BB if anyone is looking...73mm x 110mm ($30)

[Colin]

When Shimano switched from square taper to Octalink  they changed how far the cranks slid onto the spindle. The conversion necessary was to go up one size from what was stock on the bike. My 856 orginally had a 110 square taper spec'd so I installed a 113 octalink . My Evo orginally spec'd a 113 square taper so the next size up was a 118. I would say since your orginal was a 113 square taper. then if you have an octalink, ISIS or later bottom bracket, you should be using a 118.

Bu66er! So, the 73 x 113 Octalink BB I have bought to fit a FSA Carbon crank to my Oz won't fit?
I'll have to go up to a 118 ??

Can anyone else confirm this?

Of course I could just fit it and see...........

Ta
Col.

[RhinoDave]

I guess I should have been a little more specific. My information is based on using Shimano cranks with Shimano bottom brackets.. There are many variables when fitting bottom brackets with cranksets. I would recommend reading up on "Q factor" when installing different cranksets. More info here: http://www.sheldonbrown.com/bbsize.html

[orange]

I keep a store of old BB's of differing axle lengths and when I have a new frame and/or cranks I just try fitting them in turn till one fits then buy a new one in that size.

[Colin]

I keep a store of old BB's of differing axle lengths and when I have a new frame and/or cranks I just try fitting them in turn till one fits then buy a new one in that size.

That's Clever!

[Luke]

I don’t get it, unless you’re running a BMX chain the setup in your pic should work.
As suggested above, the possible combinations mean that simply talking BB length isn’t going to make much sense. I last replaced the cartridge bearings on mine (Hope ti) a couple of years ago, I didn’t measure it then, and anyway it’s super short because I’m running Middleburn RS3s.
I put the distance from the pivot to the tooth in another reply somewhere; it’s measured across the gap shown in your photo and my setup looks just like yours (just dirtier).
I’m running a 9 speed Shimano XT chain, which I’m told is the same as the Dura-ace. When I run a SRAM 9speed chain the result is the same: it works.
OK there are a few scratches on the pivot after 8 years using this setup, but nothing evil, and anyway, they blend in with the general low-maintenance philosophy of the bike (It didn’t get washed in 2007)
IMHO your derailleur’s way too low; it may be twisting the chain to get it off the ring. Once the chain is twisted it will jam. Try raising it and exaggerating the half teeth on the ring with a file; by pushing the chain against the slowly turning ring you’ll see which teeth are the upshift helpers and which are the downshift helpers. You can file them a bit more; the only reason they’re not produced sharper is the fear of law suits from idiots that manage to cut themselves “just riding down to the shop”

[purple gerbil]

luke
are you looking at same photo as us lot or wot? chain is jammed in between ring and s/arm.
and bmx chains have diff spacing of teeth and wouldnt fit into rear cassette.
the f/mech is doin its job just fine! go watch your bike changing gear.
it pulls on from rear and rotates forward until chain is fully mounted on top ring. yeah.
but if something like a swingarm gets in the way due to a b/b being a little to short then it dont work does it.
same as orange says its a case of trial and error. but if you aint blassed with a couple of different size b/b then thats that.
i would measure the distance between b/b cup and top ring on old setup and then do the same with new setup and difference
in mm is going to be what needs to be gained.
sorry for being snappy the kids ate all the darn coco pops again.(ggrrr)

say bye bye to my karma(doh)

[kiwi]

luke
are you looking at same photo as us lot or wot? chain is jammed in between ring and s/arm.

say bye bye to my karma(doh)

forgiven for current situation....luke may be looking at Colins Pics....

[Colin]

Yeah, the 3 piccies are mine, no probs with my set up! (apart from worn teeth!)
"SignalMTB" 's Piccie is attached as a file below his post.

Just measured my 4000 8 speed set up as pictured above.
Distance from face of pivot axle to centre of large chainring = 12.5mm or 1/2"

Mounting the XT FD-M750 took ages, see previous rant.......
The height is very critical, any lower and and it collides with the big chain ring, any higher and the chain rattles along the bottom of the FD cage. Probably about 1mm of correct height range. That is with 22 small ring and 44 big ring.

As New, I think you get some sort of "wedge" with a FD that locks it in the fully open position? I guess this would help immensely with the set up?

Col.

[kiwi]

Mounting the XT FD-M750 took ages, see previous rant.......
The height is very critical, any lower and and it collides with the big chain ring, any higher and the chain rattles along the bottom of the FD cage. Probably about 1mm of correct height range. That is with 22 small ring and 44 big ring.

As New, I think you get some sort of "wedge" with a FD that locks it in the fully open position? I guess this would help immensely with the set up?

Col.

yes its really a three handed job isnt it

[signalMTB]

Mounting the XT FD-M750 took ages, see previous rant.......
The height is very critical, any lower and and it collides with the big chain ring, any higher and the chain rattles along the bottom of the FD cage. Probably about 1mm of correct height range. That is with 22 small ring and 44 big ring.

which probably means even once I get the right width (ordered a 118mm today), I'm going to have height issues with my 46T ring.